Three-dimensional fabrics are already known in the art and, more particularly, are in the form of thick elements in which the fabric constituents which may be yarns, fibres, rovings, strands etc, are distributed through the fabric in three different directions which are generally perpendicular to one another but which may also have a given relative angular orientation to one another other than 90.degree.. More particularly, three-dimensional fabrics of this kind are used in certain areas of industries because of their high resistance to mechanical stresses, their thermal insulation properties and their good resistance to shocks and ablation. More particularly, recent developments in the technology of high-performance fibres or yarns, more particularly carbon fibres, silica fibres or fibres of certain plastic materials, have increased the advantage of three-dimensional fabrics, e.g. for the production of coverings for the bodies or heads of rockets or other devices or heat shields, for their protection on high-speed re-entry into atmosphere as a result of the very high heating and friction they undergo. Other applications are also under study, more particularly for the production of brake discs or plates requiring very high resistance to wear together with high heat dissipation.
Certain methods of producing such thick fabrics are already known, wherein a suitably adapted loom or weaving machine is used so that a two-directional fabric produced by a conventional weaving method and comprising, more particularly, a warp yarn and a weft yarn has a third yarn interwoven in a direction differing from the direction of the first two. Although this method may be useful when the fibres used are cotton or synthetic yarns having high tensile and flexural strength, conditions are quite different when the three-dimensional fabric has to be made by means of carbon or graphite fibres, for example, which even in the form of relatively thick rovings cannot withstand the friction of a shuttle or reed which is indispensable in weaving fabric, without breaking practically immediately.
To obviate this difficulty, it has already been proposed to make three-dimensional fabrics from graphite or carbon fibres or yarns from a graphite body or mandrel on which rigid radial rods or spikes forming one of the fabric directions are pre-machined. The other two yarn directions are made by axial weft-winding and circumferential winding between these radial spikes. Once the required fabric thickness has been obtained, the whole is rendered rigid by the incorporation of a thermosetting resin, the initial mandrel then being removed by machining or some other process, spikes to which the warp and weft yarns are connected simply being left in the thickness of the fabric. However, it will be seen that such a method is extremely expensive to use and, in particular, does not allow a high yarn density to be obtained in the radial or third direction, and this is a serious disadvantage for some applications, since the resulting fabric does not have satisfactory homogeneity and hence suitable performance in the three directions. Also, this method lends itself only with difficulty to the production of hollow bodies without any gaps, in the form of endless sleeves whose external contour or profile is a curve which may in some cases be relatively complicated.